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Tamworth Veterinary Hospital

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Snake Bite In Dogs and Cats

Introduction

Snake bites are a relatively common occurrence in regional areas of Australia. Within the Tamworth region, Brown/King brown envonomations are by far the most common. Black snake bites also occur, whilst tiger and whip snake bites are relatively uncommon. There are a number of signs which are typical of snake bites and, if observed, should be followed by prompt intensive therapy.

Clinical signs of snake envonomation

In the vast majority of snake bites, evidence of a bite wound is absent. Thus, recognition of clinical signs associated with snake bite wounds is essential if effective treatment is to be instituted. Clinical signs observed are largely dependant on the species of snake (and subsequent potency of venom) as well as the dose of venom delivered in the bite. Similarly, the clinical course of signs is also variable.

Pre-paralytic signs

Rapidity of onset of clinical signs following a snake bite is related to the dose of venom received. Generally, onset of signs is faster in dogs (1-6 hours) than cats (15 hours). Additionally, dogs commonly show pre-paralytic signs.

Pre-paralytic signs include:

  • transient collapse
  • vomiting
  • salivation
  • lethargy

Pre-paralytic signs may be followed by a seemingly spontaneous recovery. However, the presence of pre-paralytic signs almost invariably means the patient has received a lethal dose of venom, with patients usually deteriorating within hours.

In contrast, cats rarely display premonitory signs, with the earliest signs usually being weakness and ataxia.

Cats

Clinical signs obsereved in cats vary significantly. Some of these include:

  • Weakness
  • Ataxia (incoordination)

These are often the earliest signs of envonomation. Other signs also include:

  • Mydriasis (dilated pupils)
  • Vomiting
  • absence of pupillary reflex (ie pupils do not constrict in light)
  • Depression (ie quiet, unresponsive, lethargic, etc)
  • tachypnoea/dyspnoea (increased respiratory rate or difficulty breathing)
  • disorientation
  • pharyngeal paralysis
  • haematuria (blood in urine)
  • coma
  • bleeding from the bite wound

These signs are often transient and inconsistent and may not be present.

Dogs

Envonomated dogs can show an even wider array of clinical signs. Pre-paralytic signs are common. Signs of envonomation include:

  • vomiting
  • severe trembling
  • salivation
  • excitement
  • weakness
  • mydriasis (dilated pupils)
  • defecation
  • hindlimb paresis (weakness) progressing to a generalised, flaccid paralysis
  • cyanosis (gums appear blue)
  • death.

Owners often report that their dog collapsed shortly after the bite but has since recovered. This is related to the presence of pre-paralytic signs and suggests that a lethal dose of venom has been delivered to the dog. Thus, urgent treatment is required.

Diagnosis

Snake bites are largely diagnosed on suspicion given the presence of signs suggestive of a bite. Venom detection kits are available but have been found to identify the correct venom in only 42% cases. Similarly, blood samples for clotting times and PCV/TPP, urine analysis, kidney function tests, etc are also helpful in determining if a bite is likely, as well as the severity of the bite, but are not specific for snake bites.

Treatment

Treatment of snake bites revolves around prompt administration of antivenom and supportive care. Intravenous fluids, antihistamines, adrenaline and respiratory support (supplementary oxygen +/- ventilator) may all be necessary if supportive therapy is to be successful. Hospitalisation for a minimum of 24 hours is usually necessary to ensure adequate monitoring and treatment. Additional drugs (eg atropine; furosemide) may also be necessary during the course of treatment should complications arise. Antibiotics are frequently administered to avoid secondary infections.

Generally, treatment outcome is significantly improved if the animal is hospitalised and antivenom is administered. However, multiple vials of antivenom and mechanical ventilation are often required in severely envenomated animals. Thus, it must be kept in mind that cost of treatment may be high.

Patrick Byrne BVSc